GeFRO: A New Charge Sensitive Amplifier Design for Wide Bandwidth and Closed-Loop Stability Over Long Distances

A new approach was developed for the design of front-end circuits for semiconductor radiation detectors. The readout scheme is a charge sensitive amplifier, split between a very front-end stage (input transistor, feedback resistor and capacitor) located close to the detector and a remote second stage located far from the detector. The element of novelty, with respect to similar configurations, is the fact that the connecting links between the very front-end and the second stage are made with transmission lines. As a result, wide bandwidth and closed-loop stability are maintained even if the distance between the very front-end and the second stage is much larger than usual, up to tens of meters. The circuit was named GeFRO for Germanium front-end, and was tested with a BEGe detector from Canberra. Timing resolutions of 20 ns (open loop) and 185 ns (closed loop with 60 ^° phase margin) were obtained with 10 m long cables between the very front-end and the second stage. The noise of the circuit after a 10 μs Gaussian shaping was close to 160 e^- RMS with an input capacitance of 26 pF.